Scintillator including an elpasolite scintillator compound and apparatus including the scintillator

ABSTRACT

A scintillator can include an elpasolite scintillator compound. The scintillator can be doped with a Group 2 element, and may also include an activator. The scintillator has an improved core valence luminescence at room temperature as compared to a corresponding elpasolite scintillator compound without the Group 2 dopant. The elpasolite scintillator compound can have significant core valance luminescence at a temperature higher than 125° C. In a particular embodiment, the elpasolite scintillator compound can include Cl and may or may not also include another halide, such as Br or I. The scintillator can be part of an apparatus that detects gamma radiation and neutrons and may allow a relatively simpler pulse discrimination technique to be used to a higher temperature, such as 125° C. to 150° C. before a relatively more complex pulse discrimination technique would be used.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of and claims priority to U.S.patent application Ser. No. 14/885,784, entitled “SCINTILLATOR INCLUDINGAN ELPASOLITE SCINTILLATOR COMPOUND AND APPARATUS INCLUDING THESCINTILLATOR”, naming as inventors Kan Yang et al., filed Oct. 16, 2015,which application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 62/072,317, filed Oct. 29, 2014,entitled “SCINTILLATOR INCLUDING AN ELPASOLITE SCINTILLATOR COMPOUND ANDAPPARATUS INCLUDING THE SCINTILLATOR,” naming as inventors Kan Yang etal., all of which applications are assigned to the current assigneehereof and incorporated herein by reference in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure is directed to scintillators including elpasolitescintillator compounds and, apparatuses including such scintillators.

BACKGROUND

Scintillator-based detectors are used in a variety of applications,including research in nuclear physics, oil exploration, fieldspectroscopy, container and baggage scanning, and medical diagnostics.When a scintillator material of the scintillator-based detector isexposed to ionizing radiation, the scintillator material absorbs energyof incoming radiation and scintillates, remitting the absorbed energy inthe form of photons. Some scintillators are used to detect more than onetype of radiation, such as gamma radiation and neutrons. Suchscintillators may be limited in a temperature range over whichdiscrimination between the different types of radiation can effectivelyoccur.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and are not limited in theaccompanying figures.

FIG. 1 includes a depiction of a drilling apparatus.

FIG. 2 includes a depiction of a radiation detection apparatus withinthe drilling apparatus.

FIG. 3 includes a block diagram illustrating a particular embodiment ofthe analyzer device within the radiation detection apparatus of FIG. 2.

FIG. 4 includes a flow chart of a process of using the analyzer deviceof FIG. 2.

FIG. 5 includes plots of normalized intensity at room temperature forelpasolite compounds with and without a Group 2 dopant.

FIGS. 6 and 7 include plots of Fast Fourier Transform ratio as afunction of pulse height when elpasolite scintillator compounds with andwithout a Group 2 dopant are at 125° C. and exposed to a ²⁵²Cf radiationsource.

FIGS. 8 and 9 include plots of Fast Fourier Transform ratio as afunction of pulse height when elpasolite scintillator compounds with andwithout a Group 2 dopant are at 150° C. and exposed to a ²⁵²Cf radiationsource.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated relative to other elements to help to improveunderstanding of embodiments of the invention.

DETAILED DESCRIPTION

The following description in combination with the figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings.

As used herein, core valence luminescence is no longer significant whena relatively simple pulse discrimination technique cannot be used todiscriminate between neutrons and gamma radiation.

The term “corresponding elpasolite scintillator composition” is intendedto mean a scintillator compound where a Group 2 dopant is removed andreplaced by a rare element that is within the scintillator compound withthe Group 2 element. For example, Cs₂LiY_(0.98)Ce_(0.02)Cl₆ is acorresponding elpasolite scintillator composition toCs₂LiY_(0.968)Ce_(0.02)Sr_(0.012)Cl₆

The terms “comprises,” “comprising,” “includes, ” “including, ” “has, ”“having,” or any other variation thereof, are intended to cover anon-exclusive inclusion. For example, a process, method, article, orapparatus that comprises a list of features is not necessarily limitedonly to those features but may include other features not expresslylisted or inherent to such process, method, article, or apparatus.Further, unless expressly stated to the contrary, “or” refers to aninclusive-or and not to an exclusive-or. For example, a condition A or Bis satisfied by any one of the following: A is true (or present) and Bis false (or not present), A is false (or not present) and B is true (orpresent), and both A and B are true (or present).

The use of “a” or “an” is employed to describe elements and componentsdescribed herein. This is done merely for convenience and to give ageneral sense of the scope of the invention. This description should beread to include one or at least one and the singular also includes theplural, or vice versa, unless it is clear that it is meant otherwise.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The materials, methods, andexamples are illustrative only and not intended to be limiting. To theextent not described herein, many details regarding specific materialsand processing acts are conventional and may be found in textbooks andother sources within the scintillation and radiation detection arts.

A scintillator can include an elpasolite scintillator compound havingcore valence luminescence. In an embodiment, the elpasolite scintillatorcompound can be doped with a Group 2 element. The Group 2 dopant canhelp to improve core valance luminescence as compared to a correspondingelpasolite scintillator compound without a Group 2 dopant. In anotherembodiment, the elpasolite scintillator compound can have core valenceluminescence at a temperature higher than 125° C. and as high as 150° C.In an application, the scintillator can be used in an apparatus thatnormally operates over a large temperature range, for example, greaterthan 80° C. Thus, a relatively simpler pulse discrimination techniquemay be used over a larger temperature range or a higher temperaturebefore a relatively more complicated pulse discrimination is needed. Thescintillator may be used in an apparatus that can be part of a down holetool used in drilling or well logging or may be used as a port-of-entrydetector.

FIG. 1 includes a depiction of a drilling apparatus 10 includes a topdrive 12 connected to an upper end of a drill string 14 that issuspended within a well bore 16 by a draw works 17. A rotary table,including pipe slips, 18 can be used to maintain proper drill stringorientation in connection with or in place of the top drive 12. Adownhole telemetry measurement and transmission device 20, commonlyreferred to as a measurement-while-drilling (MWD) device, is part of adownhole tool that is connected to a lower end of the drill string 14.The MWD device transmits drilling-associated parameters to the surfaceby mud pulse or electromagnetic transmission. These signals are receivedat the surface by a data receiving device 22. The downhole tool includesa bent section 23, a downhole motor 24, and a drill bit 26. The bentsection 23 is adjacent the MWD device for assistance in drilling aninclined well bore. The downhole motor 24, such as apositive-displacement-motor (PDM) or downhole turbine, powers the drillbit 26 and is at the distal end of the downhole tool.

The downhole signals received by the data reception device 22 areprovided to a computer 28, an output device 30, or both. The computer 28can be located at the well site or remotely linked to the well site. Ananalyzer device can be part of the computer 28 or may be located withinthe downhole tool near the MWD device 20. The computer 28 and analyzerdevice can include a processor that can receive input from a user. Thesignals are also sent to an output device 30, which can be a displaydevice, a hard copy log printing device, a gauge, a visual audial alarm,or any combination thereof. The computer 28 is operatively connected tocontrols of the draw works 17 and to control electronics 32 associatedwith the top drive 12 and the rotary table 18 to control the rotation ofthe drill string and drill bit. The computer 28 may also be coupled to acontrol mechanism associated with the drilling apparatus's mud pumps tocontrol the rotation of the drill bit. The control electronics 32 canalso receive manual input, such as a drill operator.

FIG. 2 illustrates a depiction of a portion of the MWD device 20 withinthe downhole tool 16. The MWD device 20 includes a housing 202, atemperature sensor 204, a scintillator 222, an optical interface 232, aphotosensor 242, and an analyzer device 262. The housing 202 can includea material capable of protecting the scintillator 222, the photosensor242, the analyzer device 262, or a combination thereof, such as a metal,metal alloy, other material, or any combination thereof. The temperaturesensor 204 is located adjacent to the scintillator 222, the photosensor242, or both. The temperature sensor 204 can include a thermocouple, athermistor, or another suitable device that is capable of determiningthe temperature within the housing over the normal operating temperatureof the MWD device 20. A radiation detection apparatus includes thescintillator 222 that is optically coupled to the photosensor 242 thatis coupled to the analyzer device 262.

In an embodiment, the scintillator can include an elpasolitescintillator compound having core valence luminescence. The elpasolitescintillator compound can include a dopant of a Group 2 element of theIUPAC Periodic Table of the version of Jan. 21, 2011. For example, thedopant can include Sr, Ca, Ba, Be, Mg, or a combination thereof. In aparticular embodiment, the dopant can include Sr. In another particularembodiment, the dopant can include Ca or Ba. In a further particularembodiment, the dopant can include Mg.

In another embodiment, the elpasolite scintillator compound can have astoichiometric or a non-stoichiometric composition. For example, thecompound can have a general formula of M¹⁺ ₃RE_((1+s))X₆. M¹⁺ can be oneor more monovalent metal elements; RE can be one or more rare earthelements; X can be one or more halide elements; and−0.15<s<+0.15. In aparticular embodiment, the elpasolite scintillator compound isstoichiometric when s=0. In another particular embodiment, theelpasolite scintillator compound is non-stoichiometric when s has anon-zero value.

In a further embodiment, the monovalent metal element can include Cs,Na, K, Rb, Li, or any combination thereof. In a particular embodiment,the monovalent element can include Cs. In yet another particularembodiment, the monovalent element can include Li. In a more particularembodiment, the elpasolite scintillator compound includes both Cs andLi. As used herein, Li can be naturally occurring Li, which includesabout 8% of ⁶Li and about 92% of ⁷Li. Alternatively, Li can be enrichedwith ⁶Li so that ⁶Li makes up more than 8% of the total Li content. Forexample, ⁶Li makes up at least 70%, at least 80%, or at least 90% of thetotal Li content.

In another embodiment, the rare earth element can include Sc, Y, La, anelement of the lanthanide series of elements, or a combination thereof.In a particular embodiment, the rare earth element can include La, Lu,Y, Ga, Yb, Ce, or any combination thereof. In a more particularembodiment, the rare earth element includes Y, La, Ce, or a combinationthereof.

In yet another embodiment, the halide element can include F, Cl, Br, I,or a combination thereof. In a further embodiment, the halide elementcan include at least one atom of Cl. In a particular embodiment, thehalide element only includes Cl. In yet another embodiment, theelpasolite scintillator compound includes more than one halide elements.For example, Cl and Br, Cl and I, or Cl, Br, and I can be present.

In a particular embodiment, the elpasolite scintillator compound canhave a formula of M¹⁺ ₃RE_(1+s)Cl_((6−z))X_(z). M¹⁺ can be one or moremonovalent metal elements as described above; RE can be one or more rareearth elements as disclosed above; X can be one or more halide elementsas disclosed above; z can be in a range of 0 to 5; and −0.15<s<+0.15.

In another particular embodiment, the elpasolite scintillator compoundcan have a formula Cs₂LiRE_((1+s−x−y))Ac_(x)D_(y)X₆. RE can be one ormore rare earth elements as disclosed above; Ac can be one or moreactivators as disclosed above; D can be the dopant of a Group 2 elementas disclosed above; 0<x≦0.2; 0<y≦0.2; and −0.15<s<+0.15. In a moreparticular embodiment, 0<x≦0.1. In another more particular embodiment,0<y≦0.1 or 0<y≦0.04.

In another particular embodiment, the elpasolite scintillator compoundcan have a formula of Cs₂LiRE_((1+s−x−y))Ce_(x)D_(y)Cl₆. D can be thedopant of a Group 2 element as disclosed above; RE can include Y, La, orLu; x can be within any range disclosed above; y can be within any rangedisclosed above; and −0.15<s<+0.15. In an even more particularembodiment, RE can be Y.

In another embodiment, the elpasolite scintillator compound can includean activator. The activator can include a rare earth element asdisclosed above. Further, the activator can be a different rare earthelement than that present in the formulas disclosed above. In aparticular embodiment, the activator can include Ce, Pr, Tb, Eu, Sm, Nd,or a combination thereof. In a more particular embodiment, the activatorcan include Ce, Pr, or Tb. In an even more particular embodiment, theactivator can include Ce.

In a further embodiment, the activator can have a content of at least0.005 mol %. After reading this disclosure, a skilled artisan wouldunderstand that increasing the content of the activator may help toincrease luminescence or improve decay time of the compound. Forexample, the content can be at least 0.01 mol %, at least 0.05 mol %, atleast 0.1 mol %, or at least 0.5 mol %. In another embodiment, thecontent of the activator may be no greater than 20 mol %, which may helpto maintain charge stability of the compound. For example, the contentof the activator may be not greater than 15 mol %, not greater than 10mol %, or not greater than 5 mol %. The content of the activator can bewithin a range between any of the minimum values and maximum valuesdisclosed herein. For example, the content of the activator can be in arange of from 0.05 mol % to 10 mol % or 0.1 mol % to 5 mol %. Thecontent of the activator as disclosed herein is determined per one moleof the elpasolite scintillator compound.

In a further embodiment, the dopant as described above can have acontent of at least 0.005 mol % for the elpasolite scintillator compoundto have stronger core valence luminescent compared to a correspondingelpasolite scintillator compound that does not include the Group 2dopant. For example, the dopant content can be at least 0.007 mol %, atleast 0.01 mol %, or at least 0.02 mol %. In another embodiment, thedopant may have a content of no greater than 1 mol %, not greater than0.8 mol %, or not greater than 0.5 mol %, to help to maintain chargebalance of the compound. The content of the dopant can be within a rangeof any of the minimum values and maximum values disclosed herein. Forexample, the content of the dopant can be within a range of 0.005 mol %to 2 mol %, 0.01 mol % to 1 mol %, or 0.1 mol % to 0.5 mol %. Thecontent of the dopant as disclosed herein is determined per one mole ofthe elpasolite scintillator compound.

In still another embodiment, the elpasolite scintillator compound canfurther include a dopant that is not a Group 2 element. Such dopant canhave a content of at least 0.005 mol %, at least 0.007 mol %, or atleast 0.01 mol %. In another embodiment, the dopant may have a contentof no greater than 1 mol %, not greater than 0.8 mol %, or not greaterthan 0.5 mol %. The content of such dopant can be within a range of anyof the minimum values and maximum values disclosed herein. For example,the content of the dopant can be within a range of 0.005 mol % to 2 mol%, or 0.01 mol % to 1 mol %. In a further embodiment, such dopant caninclude a tetravalent element, which may help doping the elpasolitescintillator compound with a Group 2 element. For example, the presenceof a tetravalent dopant can help to increase the content of the Group 2dopant in the compound and maintain charge balance of the compound. Thetetravalent dopant can include Zr, Sn, or Hf. In yet another embodiment,the elpasolite scintillator compound can include a dopant of a Group 1element, a rare earth element, or a combination thereof. For example,the elpasolite scintillator compound can include a dopant including Na,Lu, or a combination thereof.

In an embodiment, the elpasolite scintillator compound disclosed hereincan have core valence luminescence. For example, the elpasolitescintillator compound can be based on Cs₂LiYCl₆ (CLYC), Cs₂LiLaCl₆(CLLC), Cs₂LiYCl_(6−z)Br_(z) (z is in a range of 0 to 5), Cs₂LiCeCl₆ orCs₂LiLuCl₆, and the activator and Group 2 dopant can be added to thesecompounds.

In a particular embodiment, exemplary elpasolite scintillator compoundcan include elpasolite scintillator compound having core valenceluminescence and including the Group 2 dopant. In a more particularembodiment, the elpasolite scintillator compound can includeCs₂LiYCl₆:Ce (CLYC:Ce) doped with Sr, Cs₂LiYCl₆:Ce (CLYC:Ce) doped withCa, Cs₂LiYCl₆:Ce (CLYC:Ce) doped with Ba, Cs₂LiLaCl₆:Ce (CLLC:Ce) dopedwith Sr, Cs₂LiLaCl₆:Ce (CLLC:Ce) doped with Ca, Cs₂LiLaCl₆:Ce (CLLC:Ce)doped with Ba, or any combination thereof.

In a further embodiment, the elpasolite scintillator compound includingthe Group 2 dopant as described above can have more core valenceluminescence compared to a corresponding elpasolite scintillatorcompound at a lower temperature such as 25° C. or a higher temperaturesuch as higher than 120° C. Stronger core valence luminescence can helpto perform pulse shape discrimination with greater accuracy.

In a further embodiment, the elpasolite scintillator compound can havecore valence luminescence at temperatures as high as 125° C. or higher.For example, temperature may be not lower than 130° C., not lower than140° C., or even not lower than 150° C.

Returning to FIG. 2, the scintillator 222 and the photosensor 242 areoptically coupled to the optical interface 232. The optical interface232 can include a polymer, such as a silicone rubber, that is used tomitigate the refractive indices difference between the scintillator 222and the photosensor 242. In other embodiments, the optical interface 232can include gels or colloids that include polymers and additionalelements.

The photosensor 242 can be a photomultiplier tube (PMT), a siliconphotomultiplier (SiPM), a hybrid photosensor, or any combinationthereof. The photosensor 242 can receive photons emitted by thescintillator 222 and produce electronic pulses based on numbers ofphotons that it receives. The photosensor 242 is electrically coupled tothe analyzer device 262. Although not illustrated in FIG. 2, anamplifier may be used to amplify the electronic signal from thephotosensor 242 before it reaches the analyzer device 262.

The analyzer device 262 can include hardware and can be at least partlyimplemented in software, firmware, or a combination thereof. In anembodiment, the hardware can include a plurality of circuits within anFPGA, an ASIC, another integrated circuit or on a printed circuit board,or another suitable device, or any combination thereof. The analyzerdevice 262 can also include a buffer to temporarily store data beforethe data are analyzed, written to storage, read, transmitted to anothercomponent or device, another suitable action is performed on the data,or any combination thereof. In the embodiment illustrated in FIG. 3, theanalyzer device 262 can include an amplifier 422 coupled to thephotosensor 242, such that an electronic pulse from the photosensor 242can be amplified before analysis. The amplifier 222 can be coupled to ananalog-to-digital converter (ADC) 424 that can digitize the electronicpulse. The ADC 424 can be coupled to a pulse shape discrimination (PSD)module 442.

In a particular embodiment, the PSD module 442 can include a FPGA or anASIC. In a particular embodiment, the PSD module 442 can includecircuits to analyze the shape of the electronic pulse and determinewhether the electronic pulse corresponds to a neutron or gammaradiation. The scintillator 222 has properties that make it well suitedfor using at high temperatures. The scintillator exhibits core valanceluminescence at a temperature higher than 125° C. In an embodiment, thecore valence luminescence can be detected at a temperature of 150° C.,and possibly higher. Thus, the PSD module 442 can use a relativelysimpler pulse discrimination technique and successfully discriminatebetween gamma radiation and neutrons before a relatively morecomplicated pulse discrimination technique would be used. An example ofchanging pulse discrimination techniques based on state information isdescribed more fully in U.S. Application No. 61/945,438 filed Feb. 27,2014, entitled “Radiation Detector, Processor Module, and Methods ofDetecting Radiation and Well Logging”, naming Kan Yang as an inventor,wherein such application is incorporated herein for its teachings ofpulse discrimination techniques and classification of detectedradiation.

In a more particular embodiment, the PSD module 442 can use theelectronic pulse and temperature from the temperature sensor 204 with alook-up table to determine whether the electronic pulse corresponds to aneutron or gamma radiation. The look-up table can be part of the FPGA orASIC or may be in another device, such as an integrated circuit, a diskdrive, or a suitable persistent memory device.

The analyzer device 262 further comprises a neutron counter 462 and agamma radiation counter 464. If the PSD module 442 determines that anelectronic pulse corresponds to a neutron, the PSD module 442 incrementsthe neutron counter 462. If the PSD module 442 determines that anelectronic pulse corresponds to gamma radiation, the PSD module 442increments the gamma radiation counter 464.

In an alternative embodiment, part or all of the components andfunctions provided by the analyzer device 262 can be located outside thewell bore, either at the well drilling site or remote to the welldrilling site, such as in an office building.

FIG. 4 includes a flowchart of an exemplary method of using the drillingapparatus as illustrated in FIG. 1 including the MWD device 20. Themethod will be described with respect to components within the drillingapparatus as illustrated in FIG. 1, the MWD device 262 as illustrated inFIG. 2, and the analyzer device as illustrated in FIG. 3. After readingthis specification, skilled artisans will appreciate that activitiesdescribed with respect to particular components may be performed byanother component. Further, activities described with respect toparticular components may be combined into a single component, andactivities described with respect to a single component may bedistributed between different components.

The method can begin with inserting the downhole tool into the well bore16, at block 502 in FIG. 4. Referring to FIG. 1, the drill bit 26 can beactivated by pumping mud down the drill string 14 to turn the downholemotor 24. For directional drilling, the orientation of the drill bit canbe controlled using the top drive 12. When the direction of drilling isto continue along a straight line, the top drive 12 rotates drill string14 while downforce pressure is exerted by the draw works 17. To changedirection, the top drive 12 is used to position the tool face of thedownhole tool. The downforce pressure may be reduced when the directionis being changed. After the toolface is in the correct position, the topdrive 12 no longer rotates the drill string, as the bent section 23causes the direction of drilling to change. The downforce pressure isincreased on the bit 26 and drilling continues as the direction changes.After the proper direction is achieved, the top drive 12 is activated torotate the drill string 14 so that further drilling continues in the newdirection. During drilling significant heat can be generated, and theresulting temperature can be greater than 120° C., at least 130° C., atleast 140° C., at least 150° C., or even higher. Also during, drillingdata is collected by the MWD device 20. The scintillator 222 is selectedso that at such temperatures, the scintillator 222 can generatedifferent scintillating light corresponding to different types ofradiation that is converted by the photosensor 242 into different typesof electronic pulses depending on the type of radiation captured.

The method can include capturing radiation and emitting scintillatinglight, at blocks 522 and 524 in FIG. 4. The radiation can be captured bythe scintillator 222, and the scintillating light can be emitted by thescintillator 222 in response to capturing the radiation. The method canfurther include generating an electronic pulse at the photosensor 242 inresponse to receiving scintillating light from the scintillator 222, atblock 542. The electronic pulse can be provided by the photosensor 242to the analyzer device 262. The method can further include amplifyingthe electronic pulse, at block 562. The electronic signal may beamplified by a pre-amplifier or an amplifier within the photosensor 242or the analyzer device 262. The method can also include converting theelectronic pulse from an analog signal to a digital signal, at block564.

The method can include determining whether electronic pulse correspondsto a neutron or gamma radiation, at block 566 in FIG. 4. In anembodiment, determination can be performed by an FPGA, an ASIC, oranother suitable device. Analysis of the pulse can include determining arise time of the pulse, a decay time, another suitable parameter thatcan be useful in making the determination, or any combination thereof.The determination can be performed using the PSD module 442. The PSDmodule 442 may use temperature information from the temperature sensor204 to determine which pulse discrimination technique should be used.The selected pulse discrimination technique can be used to analyze thepulse to determine if the pulse corresponds to a neutron or gammaradiation. The method can further include incrementing the appropriatecounter in response to the determination, at block 568. When theelectronic pulse is determined to correspond to a neutron, the neutroncounter 462 is incremented. When the electronic pulse is determined tocorrespond to gamma radiation, the gamma radiation counter 464 isincremented.

Referring to FIG. 4, some of the actions described with respect toblocks 562, 564, 566, and 568 can be performed by the analyzer device262. All of the analyzer device 262 may be within the MWD device 20 ormay be outside the well bore 16. In another embodiment, the amplifier422 and ADC 424 may be within the MWD device 20, and the PSD module 442and counters 462 and 464 may be located at the surface outside the wellbore 16. After reading this specification, skilled artisans will be ableto determine where the analyzer device or components of the analyzerdevice 262 are to be located in view of the normal operatingtemperatures, computational needs that may or may not depend on thecomposition of the scintillator, and the particular application.

While the radiation detection apparatus is described with respect to adrilling apparatus, the radiation detection apparatus can be part of awell logging apparatus that does not perform a drilling operation.Similar to the downhole tool with the drill bit 26, the well loggingapparatus can include a downhole tool without the drill bit. A flexiblestring may be coupled to the downhole tool to allow the downhole tool tolowered and raised within the well bore 16. If needed or desired a drillstring may be coupled to the downhole tool.

The scintillator and the analyzer disclosed herein can also be used as apart of a radiation detection apparatus that can be used at port entry.The scintillator and the analyzer can operate over a wide range oftemperature, such as from −40° C. to 180° C.

The concepts as described herein can be used to produce a scintillatorthat has improved core valance luminescence at room temperature andsignificant core valence luminescence at a higher temperature than acorresponding elpasolite scintillator compound. In a particularembodiment, the scintillator can be an elpasolite scintillator compoundincluding a dopant that is a Group 2 element and may or may not furtherinclude an activator. The scintillator as described herein can allow foreasier discrimination between neutrons and gamma radiation, andtherefore, a relatively simpler discrimination technique may be used,even at higher temperatures where core valence luminescence in thecorresponding elpasolite scintillator compound can no longer use therelatively simpler pulse discrimination technique. The conceptsdescribed herein may be extended to other types of radiation, such asx-rays, alpha particles, beta particles, etc. and are not limited toneutrons and gamma radiation.

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described herein. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention. Additionally, those skilled in the art willunderstand that some embodiments that include analog circuits can besimilarly implement using digital circuits, and vice versa. Embodimentsmay be in accordance with any one or more of the embodiments as listedbelow.

Embodiment 1. A scintillator including an elpasolite scintillatorcompound including a first dopant that is a Group 2 element, wherein theelpasolite scintillator compound has more core valance luminescence thana corresponding elpasolite scintillator compound without the firstdopant.

Embodiment 2. The scintillator of Embodiment 1, wherein the elpasolitescintillator compound further comprises a rare earth element.

Embodiment 3. The scintillator of Embodiment 2, wherein the elpasolitescintillator compound further comprises an activator that is differentfrom the rare earth element.

Embodiment 4. The scintillator of Embodiment 3, wherein the first dopantincludes Sr.

Embodiment 5. The scintillator of Embodiment 3,wherein the first dopantincludes Ca or Ba.

Embodiment 6. The scintillator of Embodiment 3, wherein the elpasolitescintillator has a formula of Cs₂LiRE_((1+s−x−y))Ce_(x)D^(1st) _(y)Cl₆,whereinRE includes Y, La, Ce, or Lu; D^(1st) is the first dopant;−0.15<s<+0.15; 0<x<0.2; and 0<y<0.2.

Embodiment 7. The scintillator of Embodiment 6, wherein D^(1st) is Sr.

Embodiment 8. The scintillator of Embodiment 3, wherein the activatorincludes Ce, Pr, or Tb.

Embodiment 9. The scintillator of Embodiment 1, wherein the elpasolitescintillator has a general formula of: M¹⁺ ₃RE(_(1+s))Cl_((6−z))X_(z),wherein, M⁺¹ is at least one monovalent metal element, RE is at leastone rare earth element, −0.15<s<+0.15, X is at least one halide, and zis 0 to 5.

Embodiment 10. The scintillator of Embodiment 9, wherein X includes ahalide that is different from Cl.

Embodiment 11. The scintillator of Embodiment 9, wherein thescintillator includes naturally occurring Li.

Embodiment 12. The scintillator of Embodiment 9, wherein thescintillator includes Li enriched with ⁶Li.

Embodiment 13. The scintillator of Embodiment 1, wherein thescintillator further comprises a second dopant that is a tetravalentmetal atom.

Embodiment 14. The scintillator of Embodiment 1, wherein a concentrationof the first dopant is in a range of 5×10⁻³ mol % to 0.5 mol %.

Embodiment 15. A scintillator including an elpasolite scintillatorcompound having significant core valence luminescence at a temperaturehigher than 125° C.

Embodiment 16. A radiation detection apparatus comprising a scintillatorincluding an elpasolite scintillator compound including at least onechlorine atom and a first dopant that is a Group 2 element; and aphotosensor optically coupled to the scintillator.

Embodiment 17. The apparatus of Embodiment 16, wherein the scintillatorcomprises Cs₂LiRE_((1+s−x−y))Ac_(x)D^(1st) _(y)Cl_((6−z))X_(z), whereinRE is a rare earth element other than the activator; Ac is the activatorincluding Ce, Pr, or Tb; D^(1st) is the first co-dopant that is a Group2 element; X is at least one halide; −0.15<s<+0.15; 0<x≦0.2; 0<y≦0.2;and 0≦z≦5.

Embodiment 18. The radiation detection apparatus of Embodiment 17,further comprising an analyzer unit configured to discriminate betweengamma radiation and neutrons.

Embodiment 19. The radiation detection apparatus of Embodiment 16,wherein the analyzer unit is analyzer unit configured to discriminatebetween gamma radiation and neutrons at a temperature in a range of −40°C. to 180° C.

Embodiment 20. The radiation detection apparatus of Embodiment 16,wherein the radiation detection apparatus is part of a downhole toolconfigured to be inserted into a well bore.

EXAMPLE

The Example is given by way of illustration only and do not limit thescope of the present invention as defined in the appended claims. TheExample demonstrates improved scintillator performance and pulsediscrimination when an elpasolite scintillator is doped with a Group 2element.

Data was collected on a scintillator compound with and without a Group 2dopant. The scintillators included Cs₂LiY_(0.98)Ce_(0.02)Cl₆ (CLYC:Ce)and Cs₂LiY_(0.968)Ce_(0.02)Sr_(0.012)Cl₆(CLYC:Ce;Sr). FIG. 5 includesnormalized intensity of an electronic pulse generated at 25° C. inresponse to capturing gamma radiation. CLYC:Ce;Sr has a more intensepeak as compared to CLYC:Ce. Thus, at 25° C. (room temperature),CLYC:Ce;Sr has improved core valence luminescence as compared toCLYC:Ce.

The scintillators were exposed to ²⁵²Cf having a mass of approximately109 nanograms and placed about 30 cm from the scintillator. The exposurewas performed at 125° C. and 150° C. Radiation captured by thescintillators caused scintillating light to be emitted that wascollected by a photosensor, which in turn generated an electronic pulse.A fast Fourier transform (FFT) can be performed on a portion of thepulses where the distinction between the different types of radiation isbelieved to be the greatest.

The plots as illustrated in FIGS. 6 and 7 include the FFT ratio forCLYC:Ce and CLYC:Ce;Sr, respectively when the scintillator is at 125° C.Gamma radiation are the data that extend from the upper left-hand cornerand curves toward the lower right-hand corner. For CLYC:Ce, FIG. 6illustrates that neutrons substantially overlap the portion thatcorresponds to gamma radiation. For CLYC:Ce;Sr, FIG. 7 illustrates thatneutrons are almost completely outside the portion that corresponds togamma radiation. Neutrons can be more readily discerned from gammaradiation for CLYC:Ce;Sr as compared to CLYC:Ce. At 125° C., CLYC:Ce isat the limit of the analyzer module's ability to discrimination betweenneutrons and gamma radiation using a relatively simple pulsediscrimination technique.

The plots as illustrated in FIGS. 8 and 9 include the FFT ratio forCLYC:Ce and CLYC:Ce;Sr, respectively when the scintillator is at 150° C.For CLYC:Ce, FIG. 8 illustrates that neutrons is almost entirely withinthe portion that corresponds to gamma radiation. Thus, the analyzermodule cannot use a relatively simple pulse discrimination technique fordiscriminating between neutrons and gamma radiation. A more complicatedpulse discrimination technique will be needed to discriminate betweenneutrons and gamma radiation. For CLYC:Ce;Sr. FIG. 9 illustrates thatneutrons significantly overlap the portion that corresponds to gammaradiation. Unlike CLYC:Ce, the analyzer module can still use arelatively simple pulse discrimination technique to discriminate betweenneutrons and gamma radiation for CLYC:Ce;Sr.

Accordingly, a scintillator that is an elpasolite scintillator with corevalence luminescence can be operated at a temperature higher than 125°C. and up to 150° C., possibly higher and still allow an analyzer moduleto use a relatively simple pulse discrimination technique todiscriminate accurately between neutrons and gamma radiation.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed is not necessarily the order inwhich they are performed.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

The specification and illustrations of the embodiments described hereinare intended to provide a general understanding of the structure of thevarious embodiments. The specification and illustrations are notintended to serve as an exhaustive and comprehensive description of allof the elements and features of apparatus and systems that use thestructures or methods described herein. Certain features, that are forclarity, described herein in the context of separate embodiments, mayalso be provided in combination in a single embodiment. Conversely,various features that are, for brevity, described in the context of asingle embodiment, may also be provided separately or in asubcombination. Further, reference to values stated in ranges includeseach and every value within that range. Many other embodiments may beapparent to skilled artisans only after reading this specification.Other embodiments may be used and derived from the disclosure, such thata structural substitution, logical substitution, or another change maybe made without departing from the scope of the disclosure. Accordingly,the disclosure is to be regarded as illustrative rather thanrestrictive.

What is claimed is:
 1. A scintillator, comprising an elpasolitescintillator compound represented by a general formula of M¹⁺₃RE_((1+s))X₆, wherein: M¹⁺ comprises a monovalent metal element; REcomprises a rare earth element; X comprises a halogen; and−0.15<s<+0.15.
 2. The scintillator of claim 1, wherein the elpasolitescintillator compound further comprises an activator that is differentfrom the rare earth element.
 3. The scintillator of claim 2, wherein theactivator includes Ce, Pr, or Tb.
 4. The scintillator of claim 1,wherein the elpasolite scintillator compound further comprises a firstdopant including a Group II element.
 5. The scintillator of claim 4,wherein the first dopant includes Sr.
 6. The scintillator of claim 4,wherein the first dopant includes Ca or Ba.
 7. The scintillator of claim4, wherein a concentration of the first dopant is in a range of 5×10⁻³mol % to 0.5 mol %.
 8. The scintillator of claim 1, wherein themonovalent metal element comprises Cs, Na, K, Rb, Li, or any combinationthereof
 9. The scintillator of claim 1, wherein the monovalent metalelement includes naturally occurring Li.
 10. The scintillator of claim9, wherein the monovalent metal element includes Li enriched with ⁶Li.11. A radiation detection apparatus, comprising: the scintillator ofclaim 1; a photosensor optically coupled to the scintillator; and ananalyzer device, wherein the analyzer device is configured todiscriminate between gamma radiation and neutrons.